This part of IEC 61051 is a sectional specification and is applicable to metal oxide varistors with symmetrical voltage-current characteristics for use in electronic equipment connected to any AC or DC supply system. These varistors are designed to protect electronic and other sensitive equipment from high transient surges. Varistors under the scope of this sectional specification are not intended to give primary protection against lightning surges. These varistors have metallic connections and are intended to be mounted as through hole component or directly on to printed boards. The object of this document is to prescribe preferred ratings and characteristics and to select from IEC 61051-1 the apropriate quality assessment procedures, tests and measuring methods, and to give general performance requirements for this type of varistors. Test severities and requirements prescribed in detail specifications referring to this sectional specification should be of equal or higher performance level, because lower performance levels are not permitted.